Method of recovering cellulose



United States Patent 2,743,220 I p METHOD OF RECOVERI'NG: CELLUEOSEJoseph F. Estes,,New York, N. Y.

No Drawing. Applio'ation January lti, 1952, Serial No.. 266,799

4 Claims. (CUM-56).

This invention relates-to a method of. recovering. cellu: lose and theresultant product.

An object of this invention is to providegan, improved method ofrecovering pure cellulose-from,-cellulose containing materials such asbaggasse, hemp or flax hurds, sisal or abaca, waste, or othercellulosic: material.

Another object of this invention is to, providean improved method, ofrecovering pure cellulose in finely divided form without any cellulosein, fibrous form, the recovered cellulose being free ofi discoloration.

A further object of this; invention is to.provide an improved method oftreating material containing beta and gamma cellulose aswellas alphacellulose, to-recover ahomogeneous product in particulate form, whichretains substantially the content of beta and gamma cellulose of thetreated material.

Still another object ofthis invention. is. to. provide an improvedmethod of recoveringpurecellulose from waste cellulosic material Wheresuch material is preliminarily treated: in a manner. to avoid: loss. Offbeta and gamma cellulose While removing. impurities. therefrom.

Still. a further. object of this inventionv is to-provide a novel formof cellulose which is in finely divided particulate form, comprises theseveral forms of cellulose found in the cellulosic material from. whichthe novel cellulose is derived, isaltogether .freeof'cellulose in'fiberform and is particularly adapted to be processed: into filamentary form,plastic,, filrn, gunpowder and the like, without the need for filteringoperations. 7

Yet another object ofthisin-vention is to provide an improved method oftreating waste cellulosic products to convert the same into a form whichmay be readily and, economically processed to recover pure cellulose 7therefrom.

Yet another object ofthis invention is to provide an improvedelectrolytic method of recovering pure, undiscolored cellulose fromcellulosic solutions.

Other objects of this invention will in part be obvious and in parthereinafter pointed out.

The method embodying the invention comprises essentially the use of anovel solution for quickly and readily dissolving various forms ofcellulosic material of the waste type such as baggasse, hemp and flaxhurds, sisal and abaca waste or the like, as well as other forms ofcellulose such as cotton or ramie fiber.

Such a solution comprises essentially the reaction product of a metalsalt, ammonium chloride and sodium hydroxide which isdissolved inammonium hydroxide. The resultant solution dissolves substantial amountsof cellulosic material, which may have been previously treated to effectthe removal of lignin and other impurities only and leaving the beta andgamma cellulose content thereof.

The cellulose solution is electrolyzed in a cell having a copper cathodeand a copper bearing anode with the pure cellulose depositing as agelatinous mass on the anode. The anode is periodically removed from thecell, the deposited cellulose being removed therefrom, washed 2,743,220Patented Apr. 24, 1956 A solution is prepared for dissolving cellulosecontainingmaterial, in the manner more specifically described. in

application Serial No. 266,800, filed January 16, 1952,"

Such solution may be made by preparing a saturated solution of a metalsalt such as copper sulfate, as by dissolving about 2 pounds of the saltin a gallon of water and adding thereto about 0.2 pound of ammoniumchloride. A concentrated solution of sodium hydroxide is lso. p p re byg. yd xi e t. h at f. bo 0.5 pound to a quart of water. The sodiumhydroxide solution is then added slowly to the copper salt solution withconstant stirring to form an apple green precipitate. Such precipitateis washed with water and is dissolved in a concentrated ammoniumhydroxide solution, The resultant solution is decanted to separatethesame from any undissolved residue. The ammonium chloride used amountsto not less than 5% by weight of the copper sulfate.

Various cellulose containing materials may be used with the process ofthe instant invention, including bag gasse, hemp and flax hurds, sisal;and abaca Waste, or thelike. Thus, baggasse is dissolved the solution.in the proportion of about lOparts in about 20 parts solvent, by weight.Solution takes place fairly rapidly.

The prepared cellulose solution is electrolyzed in v a manner morecompletely described in application Serial No. 267,173 filed January 18,1952. Essentially, the electrolytic cell used comprises a pair of fixedcathodes of copper with an anode located between the cathodes to receivethe cellulose deposit. Such anode when formed of. a copper-bearing irjonhaving'the following analysis: irjon-.99.874; carbon..0ll;manganese-.017; sulfur- .032; phosphorus-.008; copper-a030, andgases..028, all per cent, produces aproductfree of any discoloration.Direct current is supplied to the electrodes of the .cell ata currentdensity of about 1'0 amp res per square foot of exposed anodesurfacaandat about 6 volts.

Cellulose willbe deposited in the form of a. gelatinous mass, on theanode and when, a layer of suitable thick nessis formed, the anode isadapted to be removed from the cell to permit the removal of, thedeposited material, which is then washed with water to remove chemicalsand foreign matter. The washed material is dried to form a finelydivided, particulate material of a homogeneous nature, which isdistinguished by having a content of beta and gamma cellulosesubstantially in the proportions as the same exists in the baggassetreated. Furthermore, the product is entirely free of cellulose in fiberform.

In order to free the baggasse of a major portion of its lignin content,as well as other non-cellulosic impurities, the baggasse may bepretreated with a weak solution of sodium sulfite, sodium sulfate orammonium carbonate. Such solution may have a concentration of about 2%and the baggasse may be cooked in such solution for not more than about1 hour. In this manner while the lignin is at least partially removed,together with other non-cellulosic impurities, beta and gamma celluloseis retained. Any residual lignin left in the baggasse will deposit outin the bottom of the electrolytic cell as a sludge, which isperiodically removed from the cell.

. In the case of other cellulose containing materials, such as abacawaste, the pretreatment may include a 5% solution of sodium sulfite orthe like, but the treating period does not have to extend over 1 hour.With cotton rags,

the pretreatment is unnecessary since the clean rags may 3 ratio ofabout 2 parts of rags to 20 parts of solution, by weight.

In electrolyzing the cellulose solution, current densities may rangebetween about 5 amperes to amperes per square foot of exposed anodesurface. Voltages may vary between 2 to 12 volts, the voltage beingdetermined by the spacing between the anode and the cathodes. With lowamperages, the deposited cellulose will be of a slightly rubbery nature.

While the cellulose dissolving solution may be made up with a coppersalt, Zinc or nickel salts, such as the chlorides, sulfates, or the likemay also be used, either singly or in combination. The sodium hydroxideused to precipitate the metal salts may have a concentration varyingbetween about 20% and 35%. The ammonium hydroxide solutions used mayhave a concentration varying between about and It will be apparent thata variety of cellulose containing materials may be readily and quicklydissolved with little or no pretreatment thereof, so that cellulose inpure form may be readily recovered at a minimum cost. Furthermore, betaand gamma cellulose, heretofore lost in the pretreating fiber cookingoperation, is retained in the final product. In addition, theelectrolytic recovery of the cellulose produces a product which is notonly free of discoloration, but is also devoid of cellulose in fiberform. Thus the product may be further processed and chemically modifiedto convert the same into rayon, gun powder, film, plastic and otherforms without the need for filtering equipment to remove undesirablefibrous cellulose.

It has also been found that the homogeneous cellulose product of theinstant invention readily and quickly reacts With nitrating, acetylatingand other chemical modifying agents so as to further reduce the need forextensive treating installations. The process also allows the moreextensive use of waste cellulose products as a source for purecellulose, inasmuch as the cost of treatment is substantially reduced.

It is to be understood that the foregoing is illustrative of theinvention and that different embodiments may be made thereof Withoutdeparting from the spirit of the invention and therefore it is notintended to be limited thereby except as indicated in the claimsfollowing.

Having thus described my invention, I claim as new and desire to protectby Letters Patent:

1. The method of recovering pure cellulose from cellulose containingmaterial comprising providing an ammonium hydroxide solution of areaction product of green copper hydroxide and ammonium chloride,dissolving said material in said solution and electrolysing saidsolution in a cellhaving an iron anode containing about 0.3% copper anda copper cathode.

2. The method of recovering cellulose from cellulose containingmaterial, comprising dissolving the material in a solution containing acopper hydroxide ammonium chloride complex, and electrolyzing saiddissolved material in a cell including a copper cathode and an ironanode containing about .03% copper with a current having a density offrom about 5 to 20 amperes per square foot of anode surface.

3. The method of forming fiber free cellulose in finely dividedparticulate form from cellulose containing material comprising mixing asaturated copper sulfate solution containing ammonium chloride withconcentrated sodium hydroxide to form a green precipitate, dissolvingthe said precipitate in ammonium hydroxide to form a solution,dissolving the cellulose containing material in said solution,electrolyzing said cellulose solution in a cell having a copper cathodeand an iron anode containing a very small amount of copper at a currentdensity of about 10 amperes per square foot of anode surface, removingthe cellulose deposited on the anode and washing and drying thecellulose.

4. The method of recovering cellulose from waste cellulosic materialhaving a content of beta and gamma cellulose comprising mixing asaturated copper sulfate solution containing a small amount of ammoniumchloride with a 20% sodium hydroxide solution to form a greenprecipitate, dissolving the precipitate in ammonium hydroxide,dissolving the Waste cellulosic material in the resultant solution,electrolyzing the cellulose solution in a cell with copper cathodes andan iron anode containing about .03% copper at a current density of fromabout 5 to about 20 amperes per square foot of anode surface and fromabout 2 to 12 volts.

References Cited in the file of this patent UNITED STATES PATENTS908,937 Bayliss et a1 Jan. 5, 1909 1,590,606 Taylor June 29, 19261,851,008 Hanson et al Mar. 29, 1932 1,880,045 Richter Sept. 27, 19322,045,345 Dreyfus June 23, 1936 2,269,665 Herbst Jan. 13, 1942 2,298,260Kantorowicz Oct. 6, 1942 2,362,528 Balz et al. Nov. 14, 1944 FOREIGNPATENTS 919,558 France Dec. 9, 1946 OTHER REFERENCES Cellulose andCellulose Derivatives; by Ott, published in 1943 by IntersciencePublishers, Inc., page 750.

Heuser: Cellulose Chemistry; 1944, pp. 3, 8, and 126.

1. THE METHOD OF RECOVERING PURE CELLULOSE FROM CELLULOSE CONTAININGMATERIAL COMPRISING PROVIDING AN AMMONIUM HYDROXIDE SOLUTION OF AREACTION PRODUCT OF GREEN COPPER HYDROXIDE AND AMMONIUM CHLORIDE,DISSOLVING SAID MATERIAL IN SAID SOLUTION AND ELECTROLYSING SAIDSOLUTION IN A CELL HAVING AN IRON ANODE CONTAINING ABOUT 0.3% COPPER ANDA COPPER CATHODE.